The present invention relates to die-casting apparatus, and particularly to apparatus for forming die cast metal parts for various machines and products, including motor vehicles.
Die-casting is being used for the manufacture of larger and larger articles Large automotive parts such as internal combustion engine blocks and the housings for automatic transmissions are now commonly manufactured with die-casting as the first step in formation of the part. Such parts have extensive and complex surfaces with close tolerances; and die-casting permits their formation in high production, eliminating costly machining operations and saving metal. Die-casting requires extreme pressures exerted on the liquid metal and large amounts of heat are released from the molten metals as they cool and change state. Massive dies are required to maintain dimensional tolerances within specified limits to make such operations economically attractive and to provide the strength to withstand the stresses resulting from high pressures and forces. The die-casting molds for such large automotive parts as automatic transmission housings are, for example, frequently seven to eight feet (2.1-2.5 meters) tall, seven to eight feet (2.1-2.5 meters) wide, and six to seven feet (1.8-2.1 meters) thick when closed. The die-casting molds must be manufactured from high-grade, high-tensile strength steel.
Such dies frequently include one stationary element, one movable element operated by the die-casting machine to close the mold, and several slidable elements referred as “slides” that move transversely of the direction of movement of the die-casting machine to provide a mold cavity, which can provide intricate and re-entrant surface configurations. The mold slides, which slide transversely of the direction of movement of the die-casting machine, are generally moved by hydraulic cylinders to their proper positions. These hydraulic cylinders have typically extended laterally outward from the die-casting machine at right angles by an additional distance at least equal to the movement dimension of the slide. By way of example, such outwardly extending hydraulic cylinders used for movement of such slides can be seen unnumbered in U.S. Pat. No. 6,761,208, in U.S. Pat. No. 5,865,241 as cylinders 38a and 38b, in U.S. Pat. No. 4,206,799 as cylinders 55, in U.S. Pat. No. 3,596,708 as cylinders 66 and 68, and in U.S. Pat. No. 3,433,292 as cylinders 56, and on one occasion a die was placed in service having a pair of piston/cylinder units for one of its plurality slides carried within one of its die elements.
The length of a typical hydraulic cylinder used for movement of a slide in an automatic transmission housing or engine block can be as long as two feet or longer including its connections-with the source of hydraulic pressure. The hydraulic cylinders used for movement of such slides often extend laterally outwardly on all four sides of a die, sometimes imposing limitations in the die casting machines in which a die can be used. The hydraulic cylinders used for movement of such slides can thus contribute to the footprint of floor space occupied by a die-casting operation and are exposed to possible damage by nearby material handling and other industrial operations.
In addition, the long piston/cylinder units require heavy supporting structures extending outwardly from the die to not only carry the heavy piston/cylinder units but also withstand the stresses imposed on the supporting structures by the piston/cylinder units and their operations.
The hydraulic cylinders used for movement of such slides also require hydraulic couplings leading to flexible hoses typically attached at both ends of the hydraulic cylinders to provide for a typical double action of the pistons within the cylinders to cause both inward and outward motion of the slides with respect to the cavity in which the die-cast article is to be formed. The hoses and couplings are further coupled to valves and controllers that are located adjacent to the die-casting machine. The exposed hoses and couplings are thus also exposed to a variety of impacts and abrasions that can easily damage them to the point that any safety margin provided in prudent design can be exceeded and may result in a hydraulic failure, damage to the die, injuries to personnel, downtime and contribute to a whole range of consequences.
Furthermore, the hydraulic hoses are made from materials that expand when exposed to the high hydraulics pressures frequently encountered in die casting operations. For example, it is a common practice for operators of die casting dies to suddenly and repeatedly apply high pressure shocks to the hydraulic cylinders driving the slides to loosen and dislodge die cast parts that may not release from an open die cavity. The desired sudden application of high pressure to jar the stuck part from the mold cavity is dampened and delayed by the expansion of the hydraulic hoses, inhibiting the dislodging effect desired by the operator of the die.
Despite the various features and benefits of the prior die casting dies, there remains a need for a more compact, lighter and reliable die-casting die. There also remains a need for a die-casting die that has inherently higher safety margins that will reduce the number and severity of any hydraulic failures.